The invention relates to magnetic head structures and in particular to the magnetic gap portion of said structures. More specifically, the invention concerns a novel method of making a glass-gapped portion of the head.
Magnetic gap structures have been manufactured in a variety of ways using sintered ferromagnetic oxide which is most commonly known as ferrite. Normally a gap is provided between opposed planar surfaces otherwise known as pole tips of the magnetic transducing head. The fabrication of a glass spacer intermediate said faces is inherently very difficult since the distance between the opposed pole tip surfaces is typically in the order of 50 to 400 micro inches and also because a certain amount of diffusion and reaction takes place between molten glass and the ferrite which has a high solubility as to metallic oxides generally in molten glass. It is desirable to minimize such solubility and erosion of the faces to thereby avoid an irregular undefined transducing gap where there is no clear line of demarcation between the end of the magnetic ferrite and the beginning of non-magnetic glass gap. More particularly the flatness and parallelism of the faces are critical.
One method known in the prior art to avoid erosion or diffusion between the glass and the ferrite is to use a low temperature glass. A disadvantage of this method is that the glass which has a low temperature melting point inherently is softer and the polishing of the glass results in surface irregularity.
A trend in the art is to use higher melting or softening point glasses as the gap glass for a glass bonded ferrite recording head and to introduce the glass into the gap by means of capillary flow. The higher temperature glass is desirable because it is harder after cooling and accordingly more nearly matches the hardness of the ferrite. This is desirable too since the customary polishing operation will fail to irregularly affect the glass and the ferrite. In addition the higher temperature glass also avoids the problem of a change in the gap spacing if the glass bonded pole piece is sealed or potted in a second stage sealing operation to a support such as a disk file slider bearing. A problem with such higher temperature glass is however, that as the glass melting or softening point increases, the higher the temperature required for capillary flow and the increased likelihood of dissolution or erosion of the polished pole faces by the flowing glass as well as the increased likelihood of bubbles in the glass which are undesirable because of the decreased structural strength.
Efforts have been made in the art to reduce these problems by achieving capillary flow at the lowest possible temperature and in the shortest time interval.
One approach described in Burch et al. U.S. Pat. No. 3,824,685 is to sputter a thin layer of glass onto one or more discrete portions of a planar surface of each of two ferrite members. Thereafter the pole pieces are assembled and the remaining gap is filled by capillary flow in part from the apex. The quantity of glass drawn into the gap by capillary action is apparently aided by a reduced resistance to capillary flow provided by the softened glass layers within the gap. This approach is expensive because of the necessity of a separate sputtering step involving expensive equipment.
Other United States Patents disclosing a method having a very general similarity to the method in accordance with the invention include: Alex et al., U.S. Pat. No. 3,795,954; Maissel et al. U.S. Pat. No. 3,458,926; Duinker et al. U.S. Pat. No. 3,233,308; and Secrist U.S. Pat. No. 3,577,634. Also having a general relationship to the present invention is IBM Technical Disclosure Bulletin Volume 6 No. 4 September 1973 page 11.
It is a primary object of the invention to provide a method for depositing high temperature glass in the gap intermediate ferrite magnetic heads at the lowest possible temperature and in the least possible time.
It is another object of the invention to provide such a method which will not require the expense inherent in the use of sputtering, evaporation or similar deposition equipment.